The superior anti-sliding performance of pavement can provide a good adhesion for high speed vehicles and reduce traffic accidents, which is an important guarantee of road safety. For the frequent occurrence of traffic accidents, the insufficient anti-sliding ability of road surface is one main reason. However, the sliding resistances of pavement are closely related with the characteristics of texture morphology. The 18th session of the World Conference on road surface characteristics found that pavement friction mainly depended on the macro texture morphology and the micro texture morphology of road surface. The macro texture morphology with depths from 0.2 mm to 10 mm and widths from 0.5 mm to 50 mm is mainly determined by the size, shape, arrangement and other factors of aggregates. The micro texture morphology with depths less than 0.2 mm and widths less than 0.5 mm was mainly formed by asphalt mastic and the microscopic structure of aggregate surface, which is the main reason for the formation of the friction during the process of vehicles running at low speed.
The test methods of anti-sliding for asphalt pavement usually include fixed site measurement and continuous measurement. The fixed site equipments (such as: CTMeter (Circular Track Texture Meter), British Pendulum Tester, Dynamic Friction Tester, etc) need to temporarily interrupt the traffic and affect the normal traffic flow. And the severe shortcoming of continuous measurement equipments is their expensive price. However, just from the perspective of texture measurement, whether the fixed site equipments or the continuous equipments are used, it is difficult to comprehensively measure both the macro and micro texture morphology and give the composition of two kinds of texture morphology.
The test methods of texture morphology information of asphalt pavement are divided into direct measurement and indirect measurement according to the test mode, FIG. 1. Direct measurement methods contain contact surface profilometer, three-dimensional laser scanner and stered microscope, etc. But the speed of contact surface profilometer is slow and this method is only applicable to indoor measurement for limited points' detection. In addition, this method is usually used in two-dimensional linear measurement, which is difficult to achieve high precision of three-dimensional topography measurement. Three-dimensional laser scanner is not only expensive, but the measurement precision is controlled within 2 mm, which cannot meet the requirement of measurement precision for the microscopic texture topography. Based on the principle of focusing, Mahboob Kanafi, et al. evaluated the reconstruction effect of pavement three-dimensional texture topography by stered microscope and obtained a satisfactory result. However, this method needs to collect a series of images and identify the clear area by constantly moving these images, which requires large storage space. In regard of indirect measurement (such as: British Pendulum Tester, volume method and the overflow time method), although their operation is simple, they can't intuitively describe the road surface morphology due to their poor test repeatability and low test efficiency, which limit their further development on texture measurement.
The inevitable questions always existing in asphalt pavement are as follows: (1) Road surface is not an ideal Lambert model because the asphalt oil film and the mineral powder on the surface of road will cause mirror reflection leading to the formation of highlight points and noise points under the light conditions. (2) The coarse asphalt pavement will generate some blind angles forming shaded area. The traditional photometric stereo has better recovery effect for smooth and continuous Lambert model surface. But it is difficult to obtain a satisfactory reconstruction precision for the special surface like asphalt pavement. Sun et al. analyzed the factors affecting the reconstruction results of traditional three light source photometric stereo and studied the uncertainty of normal vector error. Results showed that increasing light intensity and keeping light incident direction orthogonal is helpful to reduce the uncertainty of error. The non-smooth surface was reconstructed by Horovitz et al. with the help of traditional three light source photometric stereo. The results showed that the significant variances were found in the discontinuous area. Slimane et al. and El Gendy et al. used three light source photometric stereo to measure the texture morphology of road surface. The results indicated that three light source photometric stereo could acquire the macro texture. But this method could not meet the accuracy requirement for the measurement of micro texture morphology. Liu et al. tried to use color information from true color images to restore the texture morphology of road surface. But the results still did not meet the precision requirement of micro texture morphology due to the existence of local error. Therefore, although the traditional photometric stereo has higher resolution, it is difficult to satisfy the precision requirement of the microscopic texture due to the special features of the asphalt pavement, which limits its application in the measurement of pavement texture morphology.
Three-dimensional reconstruction technique based on photometric stereo is widely used in reverse engineering, production quality control, industrial inspection and medical diagnosis because of the advantage of simplicity and high resolution. Therefore, Three-dimensional reconstruction of texture for pavement based on photometric stereo is improved in the invention. The acquisition method in the invention can obviously increase the test precision of texture morphology and acquire macro and micro texture morphology at the same time fast, accurately and repeatedly, which is essential to choose the materials for asphalt pavement, daily maintenance and pavement design.